Anionic polymerization of unsaturated monomers with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references. Great Britain published patent application 2,241,239 and related U.S. Pat. Nos. 5,331,058 and 5,362,699 describe a composition for an anionic protected functional initiator (PFI) having the structure ##STR1## wherein R.sup.1, R.sup.2, and R.sup.3 are independently selected from saturated and unsaturated aliphatic and aromatic radicals, A is a hydrocarbon bridging group containing from 1 to 25 carbon atoms and B is an alkali metal, such as lithium. These documents disclose that a problem with undesirable termination reactions can occur when using the PFI, particularly if the radicals, R.sup.1, R.sup.2, and R.sup.3 are all methyl or if together they contain less than 4 carbon atoms.
U.S. Pat. No. 5,416,168 describes a polymerization process using lithium compounds having the structure: ##STR2## wherein A" is cyclohexyl or --CR'R"--, wherein R' is a linear alkyl having from 1 to 10 carbon atoms, and R" is hydrogen or a linear alkyl having from 1 to 10 carbon atoms. This PFI also initiates polymerization of anionic polymers at much higher polymerization temperatures than previously known for PFIs and is cost effective to produce.
Unfortunately, even for the cost effective PFI of '168, it has been found that in commercial applications where polymerization cycle times of two hours or longer are possible, these initiators undergo undesirable termination reactions. The results of these undesirable termination reactions are varied and include (a) limiting the amount of polymer that can be produced from a given amount of initiator, (b) broadening the molecular weight distribution of the polymer, (c) limiting the ability to make well defined block copolymers, and/or (d) limiting the ability for postpolymerization chemistry, such as adding another functional site to the living end of the polymer chain. Therefore it would be highly desirable to develop a process which inhibits undesirable side reactions, resulting in a higher functionality in the polymer product.